it depends. double teams are kind of stupid in this game, theres only a small hit to the player being DTd, and only a small boon to the rest of the team. i am assuming your guy is up in the 18ppg plus ballpark? if not, i wouldn't even worry about it, double teaming a guy much lower than that isn't worth it for the other coach, i'd just ignore it. although i suppose technically it might makes sense to shift distro elsewhere - but only if the drop off is really close to negligible, which is rare, but it sounds like it might be in your case.
if i was worried about it (i usually am not, if i have a guy good enough to take 20 ppg, he is good enough to handle the double, too), i would probably shift him down a little bit, get him down more to like the mid, maybe low teens. i would never dump my best scorer from 20 ppg to 5 or something, that is dramatic overkill IMO.